1. Field of the Invention
The present invention relates to improvements on socket connectors for receiving a plurality of termination sockets for coaxial cables and, in particular, for coaxial cables having a small diameter and allowing high speed and large band width signal transmission.
2. Description of the Prior Art
Basically, for connecting coaxial cables to components of electrical equipment connectors and termination sockets are used which are rotationally symmetrical with respect to their longitudinal axis. The design of these termination sockets provides a resistance behavior which is substantially identical to the behavior of the cable and, moreover, also provides a good shielding effect. Rotationally symmetrical coaxial cable termination sockets are disclosed in U.S. Pat. Nos. 4,943,245, 4,923,412, and DE 37 32 520. Due to the substantially cylindrical design of these known termination sockets, they are less suitable for miniaturization. Accordingly, a socket connector for receiving a plurality of these known termination sockets merely has a rather low density with regard to the number of coaxial cable termination sockets per volume or space needed. However, the increased requirements for electrical equipment in particular information technology equipment such as in telecommunication multiplexer lead to a high signal density of connections i.e. a high number of cable connections in a limited space.
In order to design high density socket connectors for coaxial cable termination sockets it turned out that box-shaped coaxial cable termination sockets are suitable both with regard to miniaturization of the termination socket and the side-by-side arrangement of the termination sockets in a socket connector.
U.S. Pat. No. 4,762,508 discloses a socket connector for receiving box-shaped coaxial cable termination sockets. In each of the termination sockets for the coaxial cables, the two contacts (signal and ground) are arranged side-by-side and parallel and spaced apart in a housing comprising a shield. A plurality of these termination sockets are arranged in individual compartments or receiving portions of a socket connector body of insulating material. The body is inserted into an enclosure which is built of metallic material and designed to have shielding properties.
A similar design of a socket connector for a plurality of coaxial cable termination sockets is disclosed in EP-B-0 284 245. In this reference as well as in U.S. Pat. No. 6,203,369 there is described a coaxial cable termination socket having two signal contacts for the signal conductors of two coaxial cables and one common ground contact arranged between the two signal contacts and connected with the shields of the two coaxial contacts. Moreover, box-shaped coaxial cable termination sockets also known as SCI connectors (shielded controlled impedance connectors) are described in U.S. Pat. No. 5,184,965, DE-C-41 16 168, and DE-C-41 16 166.
A certain disadvantage of coaxial cable termination sockets having a box-shaped design i.e. having a design which is non-coaxial, results in a loss of signal transmission and increase of signal reflection properties of the termination socket for high frequent signals in the range of MHz.
While the box-shaped coaxial cable termination sockets basically work fine concerning high density packaging aspects, there are limits concerning the speed and frequency of the signals transmitted through the termination sockets. With higher frequency in the range of GHz the attenuation increases.
Attempts were made in the prior art to manage the above-mentioned problem by grounding or ground bussing. One possibility to do so is to interconnect the braid or shielding layer of each coaxial cable and to connect them to a metal strap as a ground contact at the connector. This arrangement does not provide positive grounding for each cable particularly with a high number of cables.
From U.S. Pat. Nos. 5,829,991, 5,775,924, 4,340,265, and EP-B-0 508 255 electrical connector for several coaxial cables are described each having grounding means in the form of clamping and gripping elements for mechanically and, accordingly, electrically contacting the shielding layer or braid of the individual coaxial cables. However with such an arrangement it is not possible to transmit very high speed and frequency signals. Moreover, the assembly of the known socket connectors with the gripping ground means is rather time-consuming and cumbersome.
The use of a honeycomb grounding block to engage the outer conductors of several coaxial cables is disclosed in U.S. Pat. No. 4,889,500. This arrangement comprises many parts and does not meet the requirements of a cost-efficient solution for coaxial cable termination since it is expensive and complex to manufacture or assemble, respectively.
Finally, from EP-A-0 897 202, DE-C-43 44 328, and DE-A-33 41 356 it is known to contact the outer conductor of a coaxial cable by a special ground contact in the shape of a corrugated sleeve. However, the known corrugated sleeves are provided in the coaxial connectors in order to adapt the connector to coaxial cables different in diameter. In particular, the corrugated sleeves of adjacent coaxial connectors are not interconnected among each other.
Moreover, in the prior art it is known to use ground bussing strips for connecting the housings of box-like coaxial cable termination sockets. An example of such a socket connector is disclosed in U.S. Pat. No. 6,171,143 and EP-A-0 952 637. This socket connector is adapted to receive multiple coaxial cable termination sockets and includes two opposite longitudinal recesses which are adapted to expose parts of the outer conducting casings of the termination sockets. These exposed parts are contacted by a plurality of metallic fingers of two connecting elements formed like metallic strips. These connecting elements electrically connect the termination sockets with the outer casing components of the known socket connector which casing components are electrically conductive.
Moreover, from JP-A-11 074 037 another socket connector for a plurality of coaxial cable termination sockets is known having a metal housing for receiving the termination sockets. Elastic cylindrical tube-like elements wrapped by a metal layer are inserted between the termination sockets and the metal housing so as to laterally contact the row of adjacent termination sockets.
There is still the need for socket connectors for receiving a plurality of shielded cable termination sockets having ground bussing improved with regard to both electrical properties and manufacturing aspects.